Method for controlling regenerative braking of vehicle

ABSTRACT

A method for controlling regenerative braking of a vehicle is provided, in which a driving area of a motor is decided when shifting gears during regenerative braking, and an amount of regenerative braking is determined based on the decided result. The method includes a first process of deciding whether motor torque is in a constant power mode, a second process of deciding whether the motor torque is in a constant torque mode, and a third process of deciding whether the mode of the motor torque is converted into the constant torque mode from the constant power mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of priorityto Korean Patent Application No. 10-2013-0115817 filed in the KoreanIntellectual Property Office on Sep. 30, 2013, the entire contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method for controlling regenerativebraking of a vehicle. More particularly, the present disclosure relatesto a method for controlling regenerative braking, in which an amount ofregenerative braking is determined based on characteristics of a drivingmotor when shifting gears during regenerative braking of a vehiclehaving a discrete variable transmission mounted therein.

BACKGROUND

A regenerative braking technology maximizes the fuel efficiency of agreen vehicle, such as a hybrid vehicle, an electric vehicle, a fuelcell vehicle, and the like. The regenerative braking technology is atechnology to generate electrical energy by applying a reverse torque toan electric motor and using the energy generated during braking. Thus,the electrical energy generated is stored in a high-voltage battery tobe used later to power the motor. The regenerative braking technology ismostly applied to the green vehicles.

When vehicle braking is applied, a total braking amount is determined bya driver's braking request. In this case, regenerative braking takescharge of a portion of the total braking amount, and hydraulic brakingother than regenerative braking is performed. Thus, if regenerativebraking torque transmitted to wheels is accurately estimated, stablebraking can be executed without any change in deceleration.

However, in a vehicle having a discrete variable transmission mountedtherein, deceleration may vary due to the difficulty in preciselycontrolling regenerative braking when shifting gears during regenerativebraking.

As shown in FIG. 1, in the conventional method, if a driver's brakingintention is input (S10), a total braking amount is determined based onthe driver's braking intention (S11). A regenerative braking allowanceamount in the total braking amount is determined (S12), and it is thendecided whether regenerative braking is possible (S13). In a case whereregenerative braking is possible, the amount of regenerative braking isdetermined (S14), the amount of regenerative braking is compensated(S15), and a hydraulic braking amount is then determined (S16). In acase where regenerative braking is impossible, the hydraulic brakingamount is immediately determined.

In this case, it is decided whether gear shifting is made through atransmission CAN signal. In a case where the gear shifting is made, theregenerative braking amount is calculated via an actual gear ratio. Theregenerative braking amount is compensated to have a value approximateto the actual gear ratio based on a target gear step and a shiftingphase.

However, in the conventional method, as shown in FIG. 2, there may occura failure in compensating for the regenerative braking mount based on abraking degree and gear shifting. A sudden change in the hydraulicbraking amount may be caused due to a sudden change in the regenerativebraking amount. In addition, the linearity of braking may bedeteriorated due to a sudden change in deceleration sensation.

SUMMARY

The present disclosure provides a method for controlling regenerativebraking of a vehicle, in which an amount of regenerative braking isappropriately determined by considering characteristics of a motor whenshifting gears during regenerative braking of the vehicle, thusproviding stable braking without any change in deceleration.

An exemplary embodiment of the present disclosure provides a method forcontrolling regenerative braking of a vehicle, in which a driving areaof a motor is decided when shifting gears in the vehicle duringregenerative braking, and an amount of regenerative braking isdetermined.

The method includes deciding whether motor torque is in a constant powermode in order to decide the driving area of the motor.

It is decided whether motor torque is in a constant torque mode in orderto decide the driving area of the motor.

It is decided whether a motor torque mode is converted into the constanttorque mode from the constant power mode in order to decide the drivingarea of the motor.

When the motor torque is in the constant power mode, the regenerativebraking amount is determined using motor torque before torqueintervention of a transmission control unit (TCU) and a gear ratioduring gear shifting in the constant power mode.

When the motor torque is the constant torque mode, the regenerativebraking amount is determined using motor torque before torqueintervention of a transmission control unit (TCU) and a gear ratioduring gear shifting in the constant torque mode.

When the mode of the motor torque is converted into the constant torquemode from the constant power mode, the regenerative braking amount isdetermined using a virtual motor torque which is fixed to the constanttorque mode and the gear ratio during gear shifting in the modeconversion.

Another exemplary embodiment of the present disclosure provides a methodfor controlling a regenerative braking execution when shifting gears ina vehicle during regenerative braking. The method includes a firstprocess of deciding whether motor torque is in a constant power mode. Asecond process decides whether the motor torque is in a constant torquemode. A third process decides whether a mode of the motor torque isconverted into the constant torque mode from the constant power mode,wherein a regenerative braking amount is determined based on a result ofthe first to third processes.

When the motor torque is in the constant power mode, the regenerativebraking amount may be determined by REGEN_(AV) _(—) _(StadyPower)=T_(m)_(—) _(BeforeInt)*GR_(cal)*Eff_(TM), and a gear ratio during gearshifting may use a value calculated by

${{GR}_{cal} = \frac{\omega_{Tmin}}{\omega_{TmOut}}},.$

Where, GR_(cal) is the calculated gear ratio during gear shifting,ω_(TmIn) is a transmission input speed, ω_(TmOut) is a transmissionoutput speed, REGEN_(AV) _(—) _(StadyPower) is the amount ofregenerative braking in the constant power mode, T_(m) _(—) _(BeforeInt)is motor torque before torque intervention, and Eff_(TM) is atransmission efficiency.

When the motor torque is in the constant torque mode, the regenerativebraking amount may be determined by REGEN_(AV) _(—) _(StadyTorque)=T_(m)_(—) _(BeforeInt)*GR_(cal)*Eff_(TM), and a gear ratio during the gearshifting may use a value calculated by

GR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shift _ end))α T.

Where, GR_(cal) is the gear ratio during gear shifting in the constanttorque mode, GR_(before) is a gear ratio before shifting gears, a is agear ratio slope in the constant torque mode, REGEN_(AV) _(—)_(StadyTorque) is the amount of regenerative braking in the constanttorque mode, T_(m) _(—) _(BeforeInt) is motor torque before torqueintervention, and T_(shift) _(—) _(end) is a shift end time.

The gear ratio slope in the constant torque mode may be determined by

${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$

and a differential gear ratio may use a value calculated byGR_(diff)=GR_(after)−GR_(before). Where, GR_(after) is a gear ratioafter shifting gears, and ΔT_(shift) is a shift time.

When the mode of the motor torque is converted into the constant torquemode from the constant power mode, the amount of regenerative brakingmay be determined by REGEN_(AV) _(—) _(ModeChange)=T_(m) _(—)_(Virtual)*GR_(cal)*Eff_(TM), and a gear ratio during gear shifting mayuse a value calculated by

GR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shift _ end))γ T.

Where, REGEN_(AV) _(—) _(ModeChange) is the amount of regenerativebraking in the mode conversion, T_(m) _(—) _(Virtual) is a virtual motortorque which is fixed to the constant torque mode, GR_(cal) is the gearratio during gear shifting in the mode conversion, Eff_(TM) is atransmission efficiency, GR_(before) is a gear ratio before shiftinggears, γ is a gear ratio slope in the mode conversion, and T_(shift)_(—) _(end) is a shift end time.

A gear ratio slope (α) when the motor torque is in the constant torquemode may be used as the gear ratio slope (γ) in the mode conversion, andthe gear ratio slope (α) may be calculated by

$\alpha = {\frac{{GR}_{diff}}{\Delta \; T_{shift}}.}$

Where, GR_(diff) is a differential gear ratio between before and aftergear shifting, and ΔT_(shift) is a shift time.

Other aspects and exemplary embodiments of the disclosure are discussedinfra.

In the method for controlling regenerative braking according to thepresent disclosure, regenerative braking torque transmitted to wheels isappropriately controlled by determining a regenerative braking amount,based on characteristics of the motor when shifting gears duringregenerative braking of the vehicle, thus performing stable brakingwithout any change in deceleration.

The above and other features of the disclosure are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present disclosure will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated by the accompanying drawings which are givenhereinbelow by way of illustration only, and thus are not limitative ofthe present disclosure.

FIG. 1 is a flowchart illustrating a method for controlling regenerativebraking when shifting gears in a vehicle having a discrete variabletransmission mounted therein according to the related art.

FIG. 2 is a graph illustrating a problem caused by the related artmethod.

FIG. 3 is a graph illustrating characteristics of a general drivingmotor for a vehicle.

FIG. 4 is a graph illustrating a result obtained by controlling anamount of regenerative braking in a constant power mode condition ofmotor torque, as compared with the conventional method, according to thepresent disclosure.

FIG. 5 is a graph illustrating a result obtained by controlling anamount of regenerative braking in a constant torque mode condition ofmotor torque, as compared with the conventional method, according to thepresent disclosure.

FIG. 6 is a flowchart illustrating a selection method of a gear ratioslope when a mode of motor torque is changed in a method for controllingregenerative braking according to the present disclosure.

FIG. 7 is a flowchart illustrating a selection method of motor torquewhen a mode of motor torque is changed in a method for controllingregenerative braking according to the present disclosure.

FIG. 8 is a graph illustrating a result obtained by controlling anamount of regenerative braking in a mode change condition of motortorque, as compared with the conventional method, according to thepresent disclosure.

FIG. 9 is a flowchart illustrating a method for controlling regenerativebraking of a vehicle.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the disclosure. Thespecific design features of the present disclosure as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter, reference will now be made in detail to various embodimentsof the present disclosure, examples of which are illustrated in theaccompanying drawings and described below. While the disclosure will bedescribed in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit thedisclosure to those exemplary embodiments. On the contrary, thedisclosure is intended to cover not only the exemplary embodiments, butalso various alternatives, modifications, equivalents and otherembodiments, which may be included within the spirit and scope of thedisclosure as defined by the appended claims.

The present disclosure provides a method for determining and controllinga regenerative braking amount by considering characteristics of a motor,when shifting gears during regenerative braking of a vehicle having adiscrete variable transmission mounted therein. First, torquecharacteristics of the motor used in regenerative braking will bedescribed.

As known in the art, the motor is generally divided into a constanttorque area and a constant power area according to the driving speed ofthe motor. In this case, the speed of the motor, which determines twodriving areas, is referred to as a base speed (base revolution perminute (RPM)).

As shown in FIG. 3, the motor has constant torque characteristics in adriving area of the base speed or less. That is, motor torque isconstant in the constant torque area, and the absolute value of motorpower (motor torque×motor speed) constantly increases in proportion tomotor speed. In addition, the motor has constant power characteristicsin a driving area of the base speed or more. That is, the motor power isconstant in the constant power area, and the absolute value of the motortorque (motor power/motor speed) decreases in inverse proportion to themotor speed.

A regenerative braking amount estimates motor torque transmitted to awheel in regenerative braking. The regenerative braking amount may becalculated as shown in Equation 1.

REGEN_(AV) =T _(m)*GR*Eff_(TM)  [Equation 1]

Where, REGEN_(AV) is a regenerative braking amount, T_(m) is the motortorque, GR is a gear ratio, and Eff_(TM) is a transmission efficiency.

However, Equation 1 cannot be used during gear shifting due to thefollowing reasons:

First, since the motor torque is decreased by torque intervention of atransmission control unit (TCU) (transmission input torque for smoothgear shifting is requested by the TCU), the motor has other type ofmotor torque according to a gear shifting situation. Through such ashifting mechanism, it is difficult to estimate the actual torquetransmitted to the wheel using the amount of regenerative braking.

Second, the gear ratio is also changed during gear shifting. Therefore,in a case where the amount of regenerative braking is calculated asshown in Equation 1, it is impossible to estimate the actualregenerative braking torque transmitted to the wheel using the amount ofregenerative braking. In addition, hydraulic braking with a relativelyslow reaction does not estimate a target value due to a sudden change inthe regenerative braking amount, thereby causing a variation indeceleration sensation.

Accordingly, when shifting gears in regenerative braking, the amount ofregenerative braking is constantly increased during gear shifting withconsideration of the regenerative braking amount before/after gearshifting, so that hydraulic braking can estimate the target value. Inthis case, the TCU transmits regenerative braking torque as much as theamount of regenerative braking to the wheel through the torqueintervention.

A method for constantly increasing the amount of regenerative brakingwhen shifting gears during regenerative braking is as follows:

First, in order to calculate the amount of regenerative braking duringgear shifting, motor torque before the torque intervention of the TCU isused rather than the actual motor torque after the torque interventionof the TCU. Since the motor torque before the torque intervention ischanged depending on the motor speed, it is possible to estimate achange in motor torque during gear shifting. Thus, the motor torquebefore the torque intervention of the TCU is used to calculate theamount of regenerative braking. In this case, the torque intervention ofthe TCU is a transmission input torque (i.e., motor torque) which isrequested by the TCU in order to smoothly shift the gears.

The motor torque (motor torque used in the calculation of the amount ofregenerative braking) is divided into a constant power mode, a constanttorque mode, and a mode conversion according to the characteristics ofthe motor. That is, when shifting gears during regenerative braking, theamount of regenerative braking is calculated using the constant powermode, the constant torque mode, and the mode conversion according to thecharacteristics of the motor. The amount of regenerative braking isappropriately controlled using the value calculated as described above.

A method for controlling (calculating) the amount of regenerativebraking in the constant power mode will be described hereinafter.

A gear ratio in the constant power mode uses a gear ratio (GR_(cal))during gear shifting, which is calculated using a transmission inputspeed (ω_(Tmin)) and a transmission output speed (ω_(TmOut)), closest tothe actual gear ratio as shown in the following Equation 2.

The motor torque in the constant power area is changed depending on themotor speed. Hence, when the amount of regenerative braking (REGEN_(AV)_(—) _(StadyPower)) is calculated by multiplying the actual gear ratio(GR_(cal)*Eff_(TM)) and the motor torque before the torque intervention(T_(m) _(—) _(BeforeInt)) as shown in the following Equation 3, theamount of regenerative braking (REGEN_(AV) _(—) _(StadyPower)) isconstantly increased, so that it is possible to ensure decelerationsensation during gear shifting.

$\begin{matrix}{{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \\{{REGEN}_{{AV}\_ {StadyPower}} = {T_{m\_ {BeforeInt}}*{GR}_{cal}*{Eff}_{TM}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, GR_(cal) is the calculated gear ratio during gear shifting,ω_(Tmln) is the transmission input speed, ω_(TmOut) is the transmissionoutput speed, REGEN_(AV) _(—) _(StadyPower) is the amount ofregenerative braking in the constant power mode, T_(m) _(—) _(BeforeInt)is the motor torque before the torque intervention, and Eff_(TM) is atransmission efficiency.

In addition, the amount of regenerative braking (REGEN_(AV) _(—)_(StadyPower)) in the constant power mode may be calculated as shown inthe following Equation 3-1 without considering the transmissionefficiency. In a case where the amount of regenerative braking in theconstant power mode (REGEN_(AV) _(—) _(StadyPower)) is calculated asshown in Equation 3 by considering the transmission efficiency, a moreaccurate value is calculated.

REGEN_(AV) _(—) _(StadyPower) =T _(m) _(—)_(BeforeInt)*GR_(cal)  [Equation 3-1]

Referring to FIG. 4, the amount of regenerative braking during gearshifting is controlled in a constant power mode condition of the motortorque. As a result, in a case where the amount of regenerative brakingis controlled based on Equation 3, the amount of regenerative braking isconstantly increased, so that it is possible to ensure the decelerationsensation during gear shifting, as compared with the related art.

Next, a method for controlling (calculating) the amount of regenerativebraking in the constant torque mode will be described. The gear ratio inthe constant torque mode uses a gear ratio during gear shifting(GR_(cal)) increased using a gear ratio slope (α) of the followingEquation 5 in consideration of a differential ratio (or a differentialgear ratio) before/after transmission (GR_(diff) of Equation 4). In thiscase, the gear ratio during gear shifting (GF_(cal)) may be calculatedas shown in the following Equation 6.

The motor torque before the torque intervention (T_(m) _(—)_(BeforeInt)) is not changed regardless of the motor speed, and the gearratio during gear shifting (GR_(cal)) is calculated as shown in thefollowing Equation 6. Thus, in a case where the amount of regenerativebraking (REGEN_(AV) _(—) _(StadyTorque)) is calculated by multiplyingthe motor torque before the torque intervention (T_(m) _(—)_(BeforeInt)) and the calculated gear ratio during gear shifting(GR_(cal)), the amount of regenerative braking (REGEN_(AV) _(—)_(StadyTorque)) is constantly increased, so that it is possible toensure the deceleration sensation during gear shifting.

$\begin{matrix}{{GR}_{diff} = {{GR}_{after} - {GR}_{before}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack \\{\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack \\{{GR}_{cal} = {{GR}_{before} + {\int_{T = 0}^{T_{{shift}\_ {end}}}{\alpha \ {T}}}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack \\{{REGEN}_{{AV}\_ {StadyTorque}} = {T_{m\_ {BeforeInt}}*{GR}_{cal}*{Eff}_{TM}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Where, GR_(diff) is the differential ratio, GR_(after) is the gear ratioafter gear shifting, GR_(before) is the gear ratio before gear shifting,a is the gear ratio slope in the constant torque mode, ΔT_(shift) is theshift time, GR_(cal) is the calculated gear ratio during gear shifting,REGEN_(AV) _(—) _(StadyTorque) is the amount of regenerative braking inthe constant torque mode, T_(m) _(—) _(BeforeInt) is the motor torquebefore the torque intervention, Eff_(TM) is the transmission efficiency,and T_(shift) _(—) _(end) is the shift end time.

The amount of regenerative braking in the constant torque mode(REGEN_(AV) _(—) _(StadyTorque)) may be calculated as shown in thefollowing Equation 7-1 in consideration of the transmission efficiency.In a case where the amount of regenerative braking in the constanttorque mode (REGEN_(AV) _(—) _(StadyTorque)) is calculated as shown inEquation 7 by considering the transmission efficiency, a more exactvalue is calculated.

REGEN_(AV) _(—) _(StadyTorque) =T _(m) _(—)_(BeforeInt)*GR_(cal)  [Equation 7-1]

Referring to FIG. 5, the amount of regenerative braking during the gearshifting is controlled in a constant torque mode condition of the motortorque. As a result, in a case where the amount of regenerative brakingis controlled based on the value calculated through Equation 7, theamount of regenerative braking is constantly increased. Therefore, it ispossible to ensure the deceleration sensation during gear shifting, ascompared with the related art.

A method for controlling the amount of regenerative braking in the modeconversion will be described hereinafter. In other words, a method forcontrolling the amount of regenerative braking when a mode of the motoris converted from the constant power mode to the constant torque modewill be described.

In a case where the motor torque enters into the constant torque modefrom the constant power mode according to a change in motor speed whenshifting gears during regenerative braking, gear shifting is mostlyended, and simultaneously, the motor torque again enters into theconstant power mode from the constant torque mode. If the motor speed isdecreased in the constant power mode, the absolute value of the motortorque is increased, but the motor torque in the constant torque mode ismaintained regardless of the motor speed. Hence, in the mode conversionof the motor, the gear ratio during gear shifting is calculated bydistinguishing the constant torque mode from the constant power mode,and the regenerative braking amount is controlled using the calculatedgear ratio during gear shifting.

As shown in FIG. 6, during the gear shifting (S20), it is decidedwhether the motor torque enters into the constant torque mode or theconstant torque area (S21). In a case where the motor torque enters intothe constant torque mode, the gear ratio slope (a, hereinafter, referredto as a ‘constant torque gear ratio slope’) of Equation 5 is selected asa gear ratio slope (γ) in the mode conversion by considering thedifferential ratio before/after gear shifting (see Equation 2) (S22), sothat the gear ratio during gear shifting is increased with the constanttorque gear ratio slope (α). When the motor torque does not enters intothe constant torque mode, i.e., when the motor torque is in the constantpower mode, the gear ratio slope (β, hereinafter, referred to as a‘constant power gear ratio slope’) which is a value derived throughexperiments is selected as the gear ratio slope (γ) in the modeconversion (S23), so that the gear ratio during gear shifting isincreased with the constant power gear ratio slope (β).

That is, one of the constant torque gear ratio slope (α) and theconstant power gear ratio slope (β) is used as the gear ratio slope (γ)in the mode conversion, as the gear ratio slope (or gear ratio increaseslope) to calculate the amount of regenerative braking. The gear ratioduring gear shifting (GR_(cal)) in the mode conversion may be calculatedas shown in the following Equation 8.

$\begin{matrix}{{GR}_{c\; {al}} = {{GR}_{before} + {\int_{T = 0}^{T_{{shift}\; \_ \; {end}}}{\gamma \ {T}}}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Where, GR_(cal) is the gear ratio during gear shifting in the modeconversion, GR_(before) is the gear ratio before gear shifting, γ is thegear ratio slope in the mode conversion, and T_(shift) _(—) _(end) is ashift end time.

The motor torque before the torque intervention of the TCU is used asthe motor torque in the mode conversion. In the mode conversion, themotor torque during gear shifting mostly enters into the constant torquemode from the constant power mode, and then again enters into theconstant power mode as the gear shifting is ended.

According to the present disclosure, it is decided that the modeconversion of the motor torque has occurred when the motor torque duringgear shifting enters into the constant torque mode from the constantpower mode. In the mode conversion, the motor torque is driven in theconstant torque mode from the constant power mode and then again entersinto the constant power mode. Thus, a fixed motor torque value is usedwhen the motor torque is assumed to be in the constant torque mode whenthe motor torque reenters into the constant power mode. The gear ratioduring gear shifting also uses the gear ratio calculated using theconstant torque gear ratio slope (α) which is the gear ratio slope inthe constant torque mode (see Equation 8).

The fixed value is used by assuming that the motor torque is in theconstant torque mode because it is not easy to estimate an exact shiftend time due to the influence of the shift time, road condition, and anychange in environment. Since the motor is driven in the constant torquearea at an actual shift start time, the motor torque value is fixed tothe actual shift start time. Therefore, the linearity of theregenerative braking amount and the regenerative braking torquetransmitted to the wheel can be estimated as close as the actual valuesby assuming that the motor torque is in the constant torque mode and thegear ratio slope is the constant torque gear ratio slope (α).

Referring to FIG. 7, when shifting gears during regenerative braking(S30), it is decided whether the mode conversion of the motor torqueoccurs (S31). When the mode is converted into the constant power modefrom the constant torque mode, a virtual motor torque (T_(m) _(—)_(Virtual)) which is fixed to the constant torque mode during gearshifting, is used as the motor torque (S32), and the amount ofregenerative braking is calculated using the virtual motor torque value.

Subsequently, it is decided whether gear shifting is ended whilecontrolling the amount of regenerative braking (S33). When gear shiftingis ended, motor torque before the torque intervention is used (S34).When gear shifting is not ended (i.e., during gear shifting), thevirtual motor torque (T_(m) _(—) _(Virtual)) which is fixed to theconstant torque mode, is used as the motor torque during gear shifting(S32).

When the mode is not converted into the constant torque mode from theconstant power mode by deciding whether the mode conversion of the motortorque occurs during gear shifting, i.e., when the mode does not convertin the constant torque mode or in the constant power mode, the motortorque before torque intervention is used as the motor torque duringgear shifting.

When the regenerative braking amount in the mode conversion (REGEN_(AV)_(—) _(ModeChange)) is calculated by multiplying the virtual motortorque (T_(m) _(—) _(Virtual)) value and the calculated gear ratioduring gear shifting (GR_(cal)), the amount of regenerative braking inthe mode conversion (REGEN_(AV) _(—) _(ModeChange)) is constantlyincreased, so that it is possible to ensure the deceleration sensation.

REGEN_(AV) _(—) _(ModeChange) =T _(m) _(—)_(Virtual)*GR_(cal)*E_(TM)  [Equation 9]

Where, REGEN_(AV) _(—) _(ModeChange) is the amount of regenerativebraking, T_(m) _(—) _(Virtual) is the virtual motor torque which isfixed to the constant torque mode, GR_(cal) is the calculated gear ratioduring gear shifting, and Eff_(TM) is the transmission efficiency.

The amount of regenerative braking in the mode conversion (REGEN_(AV)_(—) _(ModeChange)) may be calculated as shown in the following Equation9-1 without considering the transmission efficiency. In a case where theamount of regenerative braking in the mode conversion (REGEN_(AV) _(—)_(ModeChange)) is calculated as shown in Equation 9 by considering thetransmission efficiency, a more accurate value is calculated.

REGEN_(AV) _(—) _(ModeChange) =T _(m) _(—)_(Virtual)*GR_(cal)  [Equation 9-1]

Referring to FIG. 8, the amount of regenerative braking during gearshifting is controlled in a mode conversion condition of the motortorque. As a result, in a case where the amount of regenerative brakingis controlled based on the value calculated through Equation 9, theregenerative braking amount is constantly increased, thus ensuring thedeceleration sensation during gear shifting, as compared with therelated art.

Hereinafter, a method for controlling a regenerative braking amount whenshifting gears in a vehicle will be described with reference to FIG. 9.

As shown in FIG. 9, if a driver's braking intention is input (S100), atotal braking amount is determined based on the driver's brakingintention (S110). A regenerative braking allowance amount in the totalbraking amount is determined (S120), and it is then decided whetherregenerative braking is possible (S130).

When it is determined that the regenerative braking is impossible, ahydraulic braking amount is determined similar to the total brakingamount. Once it is decided that the regenerative braking is possible, itis decided whether gear shifting of the vehicle occurs (S140), and theamount of regenerative braking is controlled according to a decidedresult.

Here, the regenerative braking allowance amount is the maximum brakingamount which can be generated through the regenerative braking of thevehicle. The amount of regenerative braking is the actual braking amountwhich is generated through the regenerative braking in the total brakingamount determined by the driver's braking intention during vehiclebraking. The amount of regenerative braking is determined and controlledas the regenerative braking allowance amount or less.

When there is no gear shifting during regenerative braking, the amountof regenerative braking is calculated/determined (S210) using the actualmotor torque and the actual gear ratio (S150). When shifting the gearsduring the regenerative braking, it is decided whether the motor torqueenters into the constant power mode (S160).

When the motor torque enters into the constant power mode, i.e., whenthe motor torque is in the constant power mode, the regenerative brakingamount is determined (S210) using the motor torque before the torqueintervention of the TCU and the gear ratio during gear shifting,calculated using and Equation 2 (S170).

In other words, when the motor torque enters into the constant powermode, the amount of regenerative braking is determined using the motortorque before the torque intervention of the TCU and the gear ratiocalculated using the transmission input speed and the transmissionoutput speed according to Equation 2. In the constant power modecondition of the motor torque, the amount of regenerative braking may becalculated using Equation 3.

In a case where the motor torque does not enter into the constant powermode, it is decided whether the motor torque enters into the constanttorque mode (S180). When the motor torque enters into the constanttorque mode, i.e., when the motor torque is in the constant torque mode,the amount of regenerative braking is determined (S210) using the motortorque before the torque intervention of the TCU and the gear ratioduring gear shifting calculated using Equation 6 (S190). In the constanttorque mode condition of the motor torque, the amount of regenerativebraking may be calculated using Equation 7.

In a case where the motor torque does not enters into the constanttorque mode, it is decided that the motor torque is under modeconversion (S200), the amount of regenerative braking is determined(S210) using the virtual motor torque which is fixed to the constanttorque mode, and the gear ratio during gear shifting, calculated usingEquation 8 (S200). In the mode conversion condition of the motor torque,the amount of regenerative braking may be calculated using Equation 9.

After the amount of regenerative braking is determined through theaforementioned procedure when shifting the gears during the regenerativebraking (S210), other braking amount except the determined amount ofregenerative braking is determined as the hydraulic braking amount(S220). That is, other braking amount obtained by subtracting thedetermined amount of regenerative braking from the total braking amountis determined as the hydraulic braking amount.

The regenerative braking and the hydraulic braking are controlledaccording to the regenerative braking amount and the hydraulic brakingamount, determined as described above, thus performing stable braking ofthe vehicle.

In the method for controlling regenerative braking according to thepresent disclosure, it is possible to maximize regenerative braking ofthe vehicle by solving a problem of the related art hybrid vehiclehaving the discrete variable transmission mounted therein, where brakingis limited due to variation in deceleration sensation when shifting thegears during regenerative braking.

Accordingly, it is possible to remarkably improve fuel efficiencywithout any increase in cost and to minimize a change in decelerationsensation, thereby ensuring user's safety and drivability.

The disclosure has been described in detail with reference to exemplaryembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the disclosure, the scope of which isdefined in the appended claims and their equivalents.

What is claimed is:
 1. A method for controlling regenerative braking ofa vehicle, in which a driving area of a motor is decided when shiftinggears in the vehicle during regenerative braking, and a regenerativebraking amount is determined.
 2. The method of claim 1, wherein it isdecided whether motor torque is in a constant power mode in order todecide the driving area of the motor.
 3. The method of claim 1, whereinit is decided whether motor torque is in a constant torque mode in orderto decide the driving area of the motor.
 4. The method of claim 1,wherein it is decided whether a mode of the motor torque is convertedinto a constant torque mode from a constant power mode in order todecide the driving area of the motor.
 5. The method of claim 2, wherein,when the motor torque is in the constant power mode, the regenerativebraking amount is determined using motor torque before torqueintervention of a transmission control unit (TCU) and a gear ratioduring gear shifting in the constant power mode.
 6. The method of claim2, wherein, when the motor torque is in the constant power mode, theamount of regenerative braking is determined by REGEN_(AV) _(—)_(StudyPower)=T_(m) _(—) _(BeforeInt)*GR_(cal), and a gear ratio duringgear shifting uses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, ω_(TmOut) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, and T_(m) _(—) _(BeforeInt) is motor torquebefore torque intervention.
 7. The method of claim 2, wherein, when themotor torque is in the constant power mode, the amount of regenerativebraking is determined by REGEN_(AV) _(—) _(StadyPower)=T_(m) _(—)_(BeforeInt)*GR_(cal)*Eff_(TM), and a gear ratio during gear shiftinguses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, ω_(TmOut) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, T_(m) _(—) _(BeforeInt) is motor torque beforetorque intervention, and Eff_(TM) is a transmission efficiency.
 8. Themethod of claim 3, wherein, when the motor torque is in the constanttorque mode, the amount of regenerative braking is determined using themotor torque before torque intervention of a transmission control unit(TCU) and a gear ratio during gear shifting in the constant torque mode.9. The method of claim 3, wherein, when the motor torque is in theconstant torque mode, the amount of regenerative braking is determinedby REGEN_(AV) _(—) _(StadyTorque)=T_(m) _(—) _(BeforeInt)*GR_(cal), anda gear ratio during gear shifting uses a value calculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shift _ end))α T,wherein GR_(cal) is the gear ratio during gear shifting in the constanttorque mode, GR_(before) is a gear ratio before gear shifting, a is agear ratio slope in the constant torque mode, REGEN_(AV) _(—)_(StadyTorque) is the amount of regenerative braking in the constanttorque mode, T_(m) _(—) _(BeforeInt) is the motor torque before torqueintervention, and T_(shift) _(—) _(end) is a shift end time.
 10. Themethod of claim 3, wherein, when the motor torque is in the constanttorque mode, the regenerative braking amount is determined by REGEN_(AV)_(—) _(StadyTorque)=T_(m) _(—) _(BeforeInt)*GR_(cal)*Eff_(TM), and agear ratio during gear shifting uses a value calculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shift _ end))α Twherein GR_(cal) is the calculated gear ratio during gear shifting,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, T_(m) _(—) _(BeforeInt) is motor torque beforetorque intervention, Eff_(TM) is a transmission efficiency, GR_(before)is a gear ratio before gear shifting, and α is a gear ratio slope in theconstant torque mode.
 11. The method of claim 9, wherein the gear ratioslope in the constant torque mode is determined by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ and adifferential gear ratio uses a value calculated byGR_(diff)=GR_(after)−GR_(before), wherein GR_(after) is a gear ratioafter gear shifting, GR_(before) is the gear ratio before gear shifting,and ΔT_(shift) is a shift time.
 12. The method of claim 4, wherein, whenthe mode of the motor torque is converted into the constant torque modefrom the constant power mode, the amount of regenerative braking isdetermined using a virtual motor torque value, which is fixed to theconstant torque mode and a gear ratio during gear shifting in the modeconversion.
 13. The method of claim 4, wherein, when the mode of themotor torque is converted into the constant torque mode from theconstant power mode, the amount of regenerative braking is determined byREGEN_(AV) _(—) _(ModeChange)=T_(m) _(—) _(Virtual)*GR_(cal), and a gearratio during gear shifting uses a value calculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shift _ end))γ T,wherein REGEN_(AV) _(—) _(ModeChange) is the amount of regenerativebraking in the mode conversion, T_(m) _(—) _(Virtual) is a virtual motortorque value, which is fixed to the constant torque mode, GR_(cal) isthe gear ratio during gear shifting in the mode conversion, GR_(before)is a gear ratio before gear shifting, γ is a gear ratio slope in themode conversion, and T_(shift) _(—) _(end) is a shift end time.
 14. Themethod of claim 4, wherein, when the mode of the motor torque isconverted into the constant torque mode from the constant power mode,the amount of regenerative braking is determined by REGEN_(AV) _(—)_(ModeChange)=T_(m) _(—) _(Virtual)*GR_(cal)*Eff_(TM) and a gear ratioduring gear shifting uses a value calculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shift _ end))γ T,wherein REGEN_(AV) _(—) _(ModeChange) is the amount of regenerativebraking in the mode conversion, T_(m) _(—) _(Virtual) is a virtual motortorque value which is fixed to the constant torque mode, GR_(cal) is thegear ratio during gear shifting in the mode conversion, Eff_(TM) is atransmission efficiency, GR_(before) is a gear ratio before gearshifting, γ is a gear ratio slope in the mode conversion, and T_(shift)_(—) _(end) is a shift end time.
 15. The method of claim 13, wherein agear ratio slope (α) when the motor torque is in the constant torquemode is used as the gear ratio slope (γ) in the mode conversion, and thegear ratio slope (α) is calculated by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ whereinGR_(diff) is a differential gear ratio between before and after gearshifting, and ΔT_(shift) is a shift time.
 16. A method for controlling aregenerative braking execution when shifting gears in a vehicle duringregenerative braking, the method comprising: a first process of decidingwhether motor torque is in a constant power mode; a second process ofdeciding whether the motor torque is in a constant torque mode; and athird process of deciding whether a mode of the motor torque isconverted into the constant torque mode from the constant power mode,wherein an amount of regenerative braking is determined based on adecided result of the first to third processes.
 17. The method of claim16, wherein, when the motor torque is in the constant power mode, theregenerative braking amount is determined using motor torque beforetorque intervention of a transmission control unit (TCU) and a gearratio during gear shifting in the constant power mode.
 18. The method ofclaim 16, wherein, when the motor torque is in the constant power mode,the amount of regenerative braking is determined by REGEN_(AV) _(—)_(StadyPower)=T_(m) _(—) _(BeforeInt)*GR_(cal), and a gear ratio duringgear shifting uses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, ω_(Tmout) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, and T_(m) _(—) _(BeforeInt) is motor torquebefore torque intervention.
 19. The method of claim 16, wherein, whenthe motor torque is in the constant power mode, the amount ofregenerative braking is determined by REGEN_(AV) _(—)_(StadyPower)=T_(m) _(—) _(BeforeInt)*GR_(cal)*Eff_(TM), and a gearratio during gear shifting uses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, ω_(TmOut) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, T_(m) _(—) _(BeforeInt) is motor torque beforetorque intervention, and Eff_(TM) is a transmission efficiency.
 20. Themethod of claim 16, wherein the motor torque is in the constant torquemode, the amount of regenerative braking is determined using motortorque before torque intervention of a transmission control unit (TCU)and a gear ratio during gear shifting in the constant torque mode. 21.The method of claim 16, wherein, when the motor torque is in theconstant torque mode, the amount of regenerative braking is determinedby REGEN_(AV) _(—) _(StadyTorque)=T_(m) _(—) _(BeforeInt)*GR_(cal), anda gear ratio during gear shifting uses a value calculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shift _ end))α T,wherein GR_(cal) is the gear ratio during gear shifting in the constanttorque mode, GR_(before) is a gear ratio before gear shifting, α is agear ratio slope in the constant torque mode, REGEN_(AV) _(—)_(StadyTorque) is the amount of regenerative braking in the constanttorque mode, T_(m) _(—) _(BeforeInt) is motor torque before torqueintervention, and T_(shift) _(—) _(end) is a shift end time.
 22. Themethod of claim 16, wherein, when the motor torque is in the constanttorque mode, the amount of regenerative braking is determined byREGEN_(AV) _(—) _(StadyTorque)=T_(m) _(—)_(BeforeInt)*GR_(cal)*Eff_(TM), and a gear ratio during gear shiftinguses a value calculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shif t _ end))α T,wherein GR_(cal) is the gear ratio during gear shifting in the constanttorque mode, GR_(before) is a gear ratio before gear shifting, a is agear ratio slope in the constant torque mode, REGEN_(AV) _(—)_(StadyTorque) is the amount of regenerative braking in the constanttorque mode, T_(m) _(—) _(BeforeInt) is motor torque before torqueintervention, T_(shift) _(—) _(end) is a shift end time, and Eff_(TM) isa transmission efficiency.
 23. The method of claim 21, wherein the gearratio slope in the constant torque mode is determined by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ and adifferential gear ratio uses a value calculated byGR_(diff)=GR_(after)−GR_(before), wherein GR_(after) is a gear ratioafter gear shifting, and ΔT_(shift) is a shift time.
 24. The method ofclaim 16, wherein, when the mode of the motor torque is converted intothe constant torque mode from the constant power mode, the amount ofregenerative braking is determined using a virtual motor torque value,which is fixed to the constant torque mode and a gear ratio during gearshifting in the mode conversion.
 25. The method of claim 16, wherein,when the mode of the motor torque is converted into the constant torquemode from the constant power mode, the amount of regenerative braking isdetermined by REGEN_(AV) _(—) _(ModeChange)=T_(m) _(—)_(Virtual)*GR_(cal), and a gear ratio during gear shifting uses a valuecalculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(shif t _ e n d))γ T,wherein REGEN_(AV) _(—) _(ModeChange) is the amount of regenerativebraking in the mode conversion, T_(m) _(—) _(Virtual) is a virtual motortorque value, which is fixed to the constant torque mode, GR_(cal) isthe gear ratio during gear shifting in the mode conversion, GR_(before)is a gear ratio before gear shifting, γ is a gear ratio slope in themode conversion, and T_(shift) _(—) _(end) is a shift end time.
 26. Themethod of claim 16, wherein, when the mode of the motor torque isconverted into the constant torque mode from the constant power mode,the amount of regenerative braking is determined by REGEN_(AV) _(—)_(ModeChange)=T_(m) _(—) _(Virtual)*GR_(cal)*Eff_(TM), and a gear ratioduring gear shifting uses a value calculated byGR_(c al) = GR_(before) + ∫_(T = 0)^(T_(sh if t _ e nd))γ T,wherein REGEN_(AV) _(—) _(ModeChange) is the amount of regenerativebraking in the mode conversion, T_(m) _(—) _(Virtual) is a virtual motortorque value which is fixed to the constant torque mode, GR_(cal) is thegear ratio during gear shifting in the mode conversion, Eff_(TM) is atransmission efficiency, GR_(before) is a gear ratio before gearshifting, γ is a gear ratio slope in the mode conversion, and T_(shift)_(—) _(end) is a shift end time.
 27. The method of claim 25, wherein agear ratio slope (α) when the motor torque is in the constant torquemode is used as the gear ratio slope (γ) in the mode conversion, and thegear ratio slope (α) is calculated by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ whereinGR_(diff) is a differential gear ratio between before and after gearshifting, and ΔT_(shift) is a shift time.
 28. The method of claim 5,wherein, when the motor torque is in the constant power mode, the amountof regenerative braking is determined by REGEN_(AV) _(—)_(StadyPower)=T_(m) _(—) _(BeforeInt)*GR_(cal), and the gear ratioduring gear shifting uses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, to ω_(TmOut) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, and T_(m) _(—) _(BeforeInt) is the motor torquebefore the torque intervention.
 29. The method of claim 5, wherein, whenthe motor torque is in the constant power mode, the amount ofregenerative braking is determined by REGEN_(Av) _(—)_(StadyPower)=T_(m) _(—) _(BeforeInt)*GR_(cal)*Eff_(TM), and the gearratio during gear shifting uses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, ω_(TmOut) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, T_(m) _(—) _(BeforeInt) is the motor torquebefore the torque intervention, and Eff_(TM) is a transmissionefficiency.
 30. The method of claim 10, wherein the gear ratio slope inthe constant torque mode is determined by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ and adifferential gear ratio uses a value calculated byGR_(diff)=GR_(after)−GR_(before), wherein GR_(after) is a gear ratioafter gear shifting, GR_(before) is the gear ratio before gear shifting,and ΔT_(shift) is a shift time.
 31. The method of claim 14, wherein agear ratio slope (α) when the motor torque is in the constant torquemode is used as the gear ratio slope (γ) in the mode conversion, and thegear ratio slope (α) is calculated by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ whereinGR_(diff) is a differential gear ratio between before and after gearshifting, and ΔT_(shift) is a shift time.
 32. The method of claim 17,wherein, when the motor torque is in the constant power mode, the amountof regenerative braking is determined by REGEN_(AV) _(—)_(StadyPower)=T_(m) _(—) _(BeforeInt)*GR_(cal), and the gear ratioduring gear shifting uses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, ω_(TmOut) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, and T_(m) _(—) _(BeforeInt) is the motor torquebefore the torque intervention.
 33. The method of claim 17, wherein,when the motor torque is in the constant power mode, the amount ofregenerative braking is determined by REGEN_(AV) _(—)_(StadyPower)=T_(m) _(—) _(BeforeInt)*GR_(cal)*Eff_(TM), and the gearratio during gear shifting uses a value calculated by${{GR}_{cal} = \frac{\omega_{TmIn}}{\omega_{TmOut}}},$ wherein GR_(cal)is the calculated gear ratio during gear shifting, ω_(Tmin) is atransmission input speed, ω_(TmOut) is a transmission output speed,REGEN_(AV) _(—) _(StadyPower) is the amount of regenerative braking inthe constant power mode, T_(m) _(—) _(BeforeInt) is the motor torquebefore the torque intervention, and Eff_(TM) is a transmissionefficiency.
 34. The method of claim 22, wherein the gear ratio slope inthe constant torque mode is determined by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ and adifferential gear ratio uses a value calculated byGR_(diff)=GR_(after)−GR_(before), wherein GR_(after) is a gear ratioafter gear shifting, and ΔT_(shift) is a shift time.
 35. The method ofclaim 26, wherein a gear ratio slope (α) when the motor torque is in theconstant torque mode is used as the gear ratio slope (γ) in the modeconversion, and the gear ratio slope (α) is calculated by${\alpha = \frac{{GR}_{diff}}{\Delta \; T_{shift}}},$ whereinGR_(diff) is a differential gear ratio between before and after gearshifting, and ΔT_(shift) is a shift time.